The former "Doctor Who" star, 33, will appear in the biopic opposite "Girls" actress Zosia Mamet, who will play Mapplethorpe's lover/confidante, rocker Patti Smith, reported Guardian online.
The biopic, titled "Mapplethorpe", is to be directed by Ondi Timoner of Russell Brand's 2015 documentary "Brand: A Second Coming" fame and she announced the new film will be a tribute to the snapper 25 years after his death.
"We'll honour #Mapplethorpe on the 25th year of his death by bringing him to life on screen," she tweeted.